Polymeric additives containing zwitterionic moieties for PVDF-based membranes

Abstract

The present invention relates to a composition suitable for manufacturing a membrane based on a vinylidene fluoride (VDF) polymer, its porous membrane, its manufacturing method and its uses, in particular for the filtration of an aqueous phase. The composition comprising a vinylidene fluoride (VDF) polymer and a polymeric additive comprising zwitterionic moieties provides excellent hydrophilic properties of the manufactured membrane.

Description

[0001] The present invention relates to a composition suitable for manufacturing a membrane based on a vinylidene fluoride (VDF) polymer, a porous membrane thereof, a method for manufacturing the same, and uses thereof, in particular for filtration in an aqueous phase. Background Art

[0002] A porous membrane is a thin object, and its key property is its ability to control the rate of permeation of chemicals through itself. This characteristic is exploited in applications such as separation applications (water and gas).

[0003] Due to the good mechanical strength, high chemical resistance, and thermal stability of fluorinated polymers, they are widely used in the preparation of microfiltration membranes and ultrafiltration membranes. Among them, partially fluorinated polymers based on vinylidene fluoride (VDF) are particularly convenient for controlling the porosity and morphology of the membranes. Membranes made of vinylidene fluoride polymers [polymer (VDF)] are hydrophobic in nature and thus have water repellency, low water permeability, and are subject to fouling by particles and proteins on their surfaces. Hydrophobicity hinders the penetration of water into the fluoropolymer membrane, and thus higher pressure is required for water permeability and more energy is consumed. Fouling temporarily or permanently reduces the permeation flux of water through the membrane, for example, in the ultrafiltration or microfiltration process.

[0004] The ability of water to permeate through a porous PVDF membrane is usually improved by making the inner surface of the inner pores hydrophilic. In addition, it is generally believed that increasing the hydrophilicity of the PVDF membrane provides better antifouling properties because proteins and other contaminants are hydrophobic in nature.

[0005] Several strategies have been adopted to make the porous PVDF membrane hydrophilic and thus make the membrane highly water-permeable and highly antifouling. Among the methods that have been adopted, methods based on the following can be cited: grafting hydrophilic substances on the membrane surface, incorporating hydrophilic comonomers into the polymer chains of the main vinylidene fluoride polymer, incorporating hydrophilic additives, etc. These methods are reviewed, for example, in Surface Modifications for Antifouling Membranes, Chemical Reviews, 2010, Vol. 110, No. 4, pp. 2448-2471. Making PVDF-based membranes hydrophilic using zwitterionic structures is part of these methods and has received the most attention.

[0006] WO 2015 / 070004 discloses a membrane containing zwitterions, in which a selective layer formed of a statistical copolymer such as p(MMA-s-SBMA) containing zwitterionic repeating units and hydrophobic repeating units is disposed on a support layer formed of a porous PVDF membrane. However, neither the durability of the resulting membrane nor their resistance to chemical aging is mentioned.

[0007] Hydrophilic additives for PVDF-based membranes are proposed in US 2018 / 0001278, which discloses comb-shaped and random zwitterionic copolymers (such as p(MMA-r-SBMA)) useful for enhancing the hydrophilicity of PVDF membranes. Compared with PVDF membranes, the resulting additive-containing PVDF membranes exhibit good antifouling properties and improved permeability. However, in order to obtain such results, a relatively large amount of additives is required, which may compromise the mechanical, chemical resistance, and economic attractiveness of PVDF membranes. In addition, there is no mention of using stock solutions prepared with solvents commonly used for preparing membranes such as N,N-dimethylacetamide (DMAc), N,N-diethylacetamide, dimethylformamide (DMF), diethylformamide, or N-methyl-2-pyrrolidone (NMP). The membranes are prepared from DMSO-based stock solutions, and DMSO is a solvent with an odor and often produces by-products when heated (such as during the dissolution step).

[0008] There is a need to develop porous membranes with controlled pore sizes and high permeability that exhibit antifouling properties. In addition, the membranes should exhibit high thermal and chemical stability, which can ensure durable characteristics. There is also a need for additives with high thermal and chemical stability that can render the PVDF membranes in which they are dispersed hydrophilic. Additionally, these additives must be easily and durably incorporated into the polyvinylidene fluoride polymer membranes to improve their hydrophilicity, water permeability, and antifouling properties over the long term without compromising the inherent properties of the polyvinylidene fluoride polymer, which are high mechanical, thermal, and chemical properties. Furthermore, the additives must be very effective hydrophilic agents for economical use, thereby avoiding any adverse effects on the mechanical, heat resistance, and chemical resistance of the porous PVDF membranes due to their excessive presence. Finally, there is a need for a stock solution containing a VDF polymer and a hydrophilic agent that is suitable for preparing hydrophilic membranes by a solvent method, such as those involving N,N-dimethylacetamide (DMAc), N,N-diethylacetamide, dimethylformamide (DMF), diethylformamide, or N-methyl-2-pyrrolidone (NMP) commonly used for preparing membranes. Summary of the Invention

[0009] The first aspect of the present invention meets all these needs and more, and the first aspect of the present invention relates to a composition [Composition (C)] comprising:

[0010] - at least one polyvinylidene fluoride (VDF) polymer [Polymer (VDF)], and

[0011] - at least one copolymer [Copolymer (N-ZW)] comprising

[0012] (a) repeating units [Units (R ZW)], and

[0013] (b) repeating units [unit (R N )] derived from at least one additional monomer [monomer (B)] different from monomer (A),

[0014] wherein, based on the molar composition of the copolymer (N-ZW), unit (R ZW ) accounts for 0.1 to 7 mol%, preferably 0.1 to 5 mol%, and

[0015] wherein the molecular weight of the copolymer (N-ZW) measured by gel permeation chromatography ranges from 25,000 g / mol to 350,000 g / mol, and

[0016] wherein the weight ratio of copolymer (N-ZW) / polymer (VDF) is at least 0.1 / 99.9 and / or less than 25 / 75.

[0017] A second aspect of the present invention relates to a method for manufacturing a porous membrane, the method comprising:

[0018] Step (i): preparing a composition (C) which further comprises at least one liquid medium [medium (L)], the at least one liquid medium comprising at least one organic solvent, [composition (C L )];

[0019] Step (ii): processing the composition provided in step (i) to provide a thin film; and,

[0020] Step (iii): processing the thin film provided in step (ii), generally comprising contacting the thin film with a non-solvent medium [medium (NS)] to provide a porous membrane.

[0021] A third aspect of the present invention relates to a porous membrane comprising:

[0022] - at least one vinylidene fluoride polymer [polymer (VDF)], and

[0023] - at least one copolymer [copolymer (N-ZW)] which comprises

[0024] (a) repeating units [unit (R ZW )] derived from at least one zwitterionic monomer [monomer (A)], and

[0025] (b) repeating units [unit (R N )] derived from at least one additional monomer [monomer (B)] different from monomer (A),

[0026] wherein, based on the molar composition of the copolymer (N-ZW), unit (RZW ) accounts for 0.1 to 7 mol%, preferably 0.1 to 5 mol%, and

[0027] the molecular weight of the copolymer (N-ZW) measured by gel permeation chromatography ranges from 25,000 g / mol to 350,000 g / mol, and

[0028] where the weight ratio of copolymer (N-ZW) / polymer (VDF) is at least 0.1 / 99.9 and / or less than 25 / 75.

[0029] The porous membrane can be obtained from the composition (C L ) as described above and manufactured by the method as described above.

[0030] The fourth aspect of the present invention relates to a method for separating an aqueous medium, the method comprising contacting the aqueous medium with the porous membrane as described above.

[0031] The applicant has unexpectedly found that the composition (C) detailed above is particularly effective for manufacturing membranes, providing excellent permeation performance during the filtration and separation of aqueous media, while still being compatible with the typical water-induced coagulation process characteristic of membrane manufacturing.

[0032] Polymer (VDF)

[0033] The expressions "vinylidene fluoride polymer" and "polymer (VDF)" are used within the framework of the present invention to indicate a polymer comprising repeating units derived from vinylidene fluoride (usually as the main repeating unit component). Thus, polymer (VDF) is generally a polymer mainly composed of repeating units, more than 50 mol% of which are derived from vinylidene fluoride (VDF).

[0034] Polymer (VDF) may further comprise repeating units derived from at least one fluorinated monomer different from VDF, and / or may further comprise repeating units derived from a non-fluorinated monomer (also referred to as a "hydrogenated monomer"). The term "fluorinated monomer" is hereby intended to denote an ethylenically unsaturated monomer containing at least one fluorine atom. The fluorinated monomer may further comprise one or more other halogen atoms (Cl, Br, I).

[0035] In particular, polymer (VDF) is generally selected from addition polymers comprising repeating units derived from VDF, and optionally repeating units derived from at least one ethylenically unsaturated monomer different from VDF containing one or more fluorine atoms, which monomer is generally selected from the group consisting of:

[0036] (a) C2-C8 perfluoroolefins, such as tetrafluoroethylene (TFE), hexafluoropropylene (HFP), perfluoroisobutene;

[0037] (b) Hydrogen-containing C2-C8 fluoroolefins different from VDF, such as vinyl fluoride (VF), trifluoroethylene (TrFE), hexafluoroisobutene (HFIB), perfluoroalkyl vinylenes having the formula CH2=CH-R f1 where R f1 is a C1-C6 perfluoroalkyl group;

[0038] (c) C2-C8 fluoroolefins containing chlorine and / or bromine, such as chlorotrifluoroethylene (CTFE);

[0039] (d) Perfluoroalkyl vinyl ether (PAVE) having the formula CF2=CFOR f1 where R f1 is a C1-C6 perfluoroalkyl group, such as CF3 (PMVE), C2F5 or C3F7;

[0040] (e) Perfluorooxyalkyl vinyl ether having the formula CF2=CFOX0, where X0 is a C1-C 12 perfluorooxyalkyl group containing one or more ether oxygen atoms, notably including perfluoromethoxyalkyl vinyl ether having the formula CF2=CFOCF2OR f2 where R f2 is a C1-C3 perfluoro(oxy)alkyl group, such as -CF2CF3, -CF2CF2-O-CF3 and -CF3; and

[0041] (f) (Per)fluorometa-dioxolene having the following formula:

[0042]

[0043] where each of R f3 , R f4 , R f5 and R f6 is the same as or different from each other and independently is a fluorine atom, a C1-C6 perfluoro(oxy)alkyl group optionally containing one or more oxygen atoms, such as -CF3, -C2F5, -C3F7, -OCF3 or -OCF2CF2OCF3.

[0044] The vinylidene fluoride polymer [polymer (VDF)] is preferably a polymer comprising:

[0045] (a’) At least 60 mol%, preferably at least 75 mol%, more preferably 85 mol% of repeat units derived from vinylidene fluoride (VDF);

[0046] (b’) Optionally from 0.1 mol% to 30 mol%, preferably from 0.1 mol% to 20 mol%, more preferably from 0.1 mol% to 15 mol% of repeat units derived from fluorinated monomers different from VDF; and

[0047] (c’) Optionally, repeating units derived from one or more hydrogenated monomers, in an amount of from 0.1% to 10% by mole, preferably from 0.1% to 5% by mole, more preferably from 0.1% to 1% by mole,

[0048] All of the above percentages by mole refer to the total number of moles of the repeating units of the polymer (VDF).

[0049] The fluorinated monomer is advantageously selected from the group consisting of: vinyl fluoride (VF1); trifluoroethylene (VF3); chlorotrifluoroethylene (CTFE); 1,2-difluoroethylene; tetrafluoroethylene (TFE); hexafluoropropylene (HFP); perfluoro(alkyl) vinyl ethers such as perfluoro(methyl) vinyl ether (PMVE), perfluoro(ethyl) vinyl ether (PEVE) and perfluoro(propyl) vinyl ether (PPVE); perfluoro(1,3-dioxolene); perfluoro(2,2-dimethyl-1,3-dioxolene) (PDD). Preferably, the possible additional fluorinated monomers are selected from chlorotrifluoroethylene (CTFE), hexafluoropropylene (HFP), trifluoroethylene (VF3) and tetrafluoroethylene (TFE).

[0050] The selection of the one or more hydrogenated monomers is not particularly limited; α-olefins, (meth)acrylic monomers, vinyl ether monomers, styrene monomers can be used; however, in order to optimize chemical resistance, embodiments in which the polymer (F) is substantially free of repeating units derived from the one or more hydrogenated comonomers are preferred.

[0051] Thus, the vinylidene fluoride polymer [polymer (VDF)] is more preferably a polymer mainly composed of:

[0052] (a’) repeating units derived from vinylidene fluoride (VDF), in an amount of at least 60% by mole, preferably at least 75% by mole, more preferably 85% by mole;

[0053] (b’) Optionally, fluorinated monomers different from VDF, in an amount of from 0.1% to 30% by mole, preferably from 0.1% to 20% by mole, more preferably from 0.1% to 15% by mole; the fluorinated monomers are preferably selected from the group consisting of vinyl fluoride (VF1), chlorotrifluoroethylene (CTFE), hexafluoropropylene (HFP), tetrafluoroethylene (TFE), perfluoromethyl vinyl ether (MVE), trifluoroethylene (TrFE) and mixtures thereof, and all of the above percentages by mole refer to the total number of moles of the repeating units of the polymer (VDF).

[0054] In addition to the repeating units, defects, end chains, impurities, chain inversions or chain branching, etc. may additionally be present in the polymer (VDF), and these components basically do not change the properties and characteristics of the polymer (VDF).

[0055] As non-limiting examples of polymers (VDF) useful in the present invention, mention may worthily be made of homopolymers of VDF, VDF / TFE copolymers, VDF / TFE / HFP copolymers, VDF / TFE / CTFE copolymers, VDF / TFE / TrFE copolymers, VDF / CTFE copolymers, VDF / HFP copolymers, VDF / TFE / HFP / CTFE copolymers, etc.

[0056] VDF homopolymers are particularly advantageous for use as polymers (VDF) in composition (C).

[0057] The melt index of the polymer (VDF) is advantageously at least 0.01, preferably at least 0.05, more preferably at least 0.1 g / 10 min and advantageously less than 50, preferably less than 30, more preferably less than 20 g / 10 min when measured according to ASTM test No. 1238 at 230 °C under a piston load of 2.16 kg.

[0058] The melt index of the polymer (VDF) is advantageously at least 0.1, preferably at least 1, more preferably at least 5 g / 10 min and advantageously less than 70, preferably less than 50, more preferably less than 40 g / 10 min when measured according to ASTM test No. 1238 at 230 °C under a piston load of 5 kg.

[0059] The melt index of the polymer (VDF) is advantageously at least 0.1, preferably at least 0.5, more preferably at least 1 g / 10 min and advantageously less than 30, preferably less than 20, more preferably less than 10 g / 10 min when measured according to ASTM test No. 1238 at 230 °C under a piston load of 21.6 kg.

[0060] The polymer (VDF) advantageously has a melting point (T m ) which is advantageously at least 120 °C, preferably at least 125 °C, more preferably at least 130 °C and at most 190 °C, preferably at most 185 °C, more preferably at most 180 °C as determined by DSC according to ASTM D3418 at a heating rate of 10 °C / min.

[0061] Copolymer (N-ZW) containing zwitterionic repeating units

[0062] Composition (C) generally comprises at least one copolymer [copolymer (N-ZW)] which comprises

[0063] (a) repeating units [units (R ZW )] derived from at least one zwitterionic monomer [monomer (A)], and

[0064] (b) repeating units [unit (R N )] derived from at least one additional monomer [monomer (B)] different from monomer (A).

[0065] Typically, zwitterionic repeating units (R ZW ) are derived from at least one zwitterionic monomer (A) that has a neutral overall charge but contains an equal number of groups (C+) and groups (A-). One or more cationic charges can be contributed by at least one of the following onium or inium cations: nitrogen, such as ammonium, pyridinium, and imidazolinium cations; phosphorus, such as phosphonium; and / or sulfur, such as sulfonium. One or more anionic charges can be contributed by at least one carbonate, sulfonate, phosphate, phosphonate, hypophosphonate, or vinyl alcoholate anion, etc. Suitable zwitterionic monomers include, but are not limited to, betaine monomers that are zwitterionic and contain an onium atom that does not carry a hydrogen atom and is not adjacent to an anionic atom.

[0066] In some embodiments, unit (R ZW ) is derived from at least one monomer (A) selected from the list consisting of:

[0067] a) Dialkylammonium alkyl acrylates or methacrylates, alkyl or hydroxyalkyl sulfonates or phosphonates of acrylamido or methacrylamido, typically

[0068] - 2-(methacryloyloxy)ethyltrimethylammonium propane-1-sulfonate,

[0069] - 2-(acryloyloxy)ethyltrimethylammonium ethane-1-sulfonate,

[0070] - 2-(methacryloyloxy)ethyltrimethylammonium butane-1-sulfonate,

[0071] - 2-(methacryloyloxy)ethyltrimethylammonium 2-hydroxypropane-1-sulfonate,

[0072] - 3-(trimethylammonio)propyl acrylamide propane-1-sulfonate,

[0073] - 3-(trimethylammonio)propyl methacrylamide propane-1-sulfonate,

[0074] - 3-(trimethylammonio)propyl 2-hydroxypropane-1-sulfonate (meth)acrylamide,

[0075] - 2-(2-(trimethylammonio)ethoxy)ethyl 2-(methacryloyloxy)ethyl sulfonate.

[0076] b) Heterocyclic betaine monomers, typically

[0077] - Sulfobetaine derived from piperazine,

[0078] - Sulfobetaines derived from 2-vinylpyridine and 4-vinylpyridine, more typically 2-vinyl-1-(3-sulfopropyl)pyridinium betaine or 4-vinyl-1-(3-sulfopropyl)pyridinium betaine,

[0079] - 1-vinyl-3-(3-sulfopropyl)imidazolium betaine;

[0080] c) Alkyl or hydroxyalkyl sulfonates or phosphonates of dialkylammonium alkyl allyls, typically sulfopropyl methyldiallylammonium betaine;

[0081] d) Alkyl or hydroxyalkyl sulfonates or phosphonates of dialkylammonium alkyl styrenes;

[0082] e) Betaines produced from ethylenically unsaturated acid anhydrides and dienes;

[0083] f) Phosphate betaines having the following formula

[0084]

[0085] ; and

[0086] g) Betaines produced from cyclic acetals, typically ((dicyanoethanolate)ethoxy)dimethylammonium propyl methacrylamide.

[0087] In some preferred embodiments, the unit (R ZW ) is derived from at least one monomer (A) selected from the list consisting of:

[0088] - Dimethylammonioethyl 3-sulfopropyl acrylate,

[0089] - Dimethylammonioethyl 3-sulfopropyl methacrylate (SPE),

[0090]

[0091] - Dimethylammoniopropyl 3-sulfopropyl acrylamide,

[0092] - Dimethylammoniopropyl 3-sulfopropyl methacrylamide,

[0093] - Dimethylammonioethyl 3-sulfohydroxypropyl acrylate,

[0094] - Dimethylammonioethyl 3-sulfohydroxypropyl methacrylate (SHPE),

[0095] - Dimethylammoniopropyl 3-sulfohydroxypropyl acrylamide (AHPS),

[0096] - Dimethylammoniopropyl 3-sulfohydroxypropyl methacrylamide (SHPP)

[0097] -1-(3-Sulfopropyl)-2-vinylpyridinium (2SPV), and

[0098]

[0099] -1-(3-Sulfopropyl)-4-vinylpyridinium (4SPV).

[0100] In some more preferred embodiments, the unit (R ZW ) is derived from at least one monomer (A) selected from the list consisting of:

[0101] -Ethyl (dimethylammonio)ethyl methacrylate sulfate,

[0102] -Ethyl (dimethylammonio)ethyl acrylate sulfate,

[0103] -1-(3-Sulfopropyl)-2-vinylpyridinium, and

[0104] -1-(3-Sulfopropyl)-4-vinylpyridinium.

[0105] In some even more preferred embodiments, the unit (R ZW ) is derived from

[0106] -Ethyl (dimethylammonio)ethyl methacrylate sulfate (SPE), or

[0107] -1-(3-Sulfopropyl)-2-vinylpyridinium (2SPV).

[0108] The copolymer (N-ZW) according to the present disclosure, in addition to comprising repeating units (R ZW ) derived from at least one zwitterionic monomer (A), further comprises repeating units (R N ) derived from at least one additional monomer (B) different from monomer (A).

[0109] Often, the unit (R N ) is derived from at least one monomer having no ionizable groups.

[0110] In some embodiments, the unit (R N ) is derived from at least one monomer selected from the list consisting of: methyl methacrylate, ethyl methacrylate, butyl methacrylate, methyl acrylate, ethyl acrylate, butyl acrylate, vinyl acetate, and N,N-dimethylacrylamide, [unit (R N-1 )]. Preferably, the unit (R N-1 ) is derived from methyl methacrylate, ethyl methacrylate or a mixture thereof. More preferably, the unit (R N-1 ) is derived from methyl methacrylate.

[0111] In some other embodiments, the unit (R N ) is derived from at least one monomer selected from the list consisting of: 2-hydroxyethyl methacrylate (HEMA), hydroxypropyl methacrylate, 2-hydroxyethyl acrylate (HEA), hydroxypropyl acrylate, 4-hydroxybutyl acrylate, poly(ethylene glycol) methacrylate (PEGMA), poly(ethylene glycol) methyl ether methacrylate (mPEGMA), poly(ethylene glycol) ethyl ether methacrylate, poly(ethylene glycol) methyl ether acrylate, and poly(ethylene glycol) ethyl ether acrylate, [unit (R N-2 )]. Preferably, the unit (R N-2 ) is derived from 2-hydroxyethyl methacrylate (HEMA), hydroxypropyl methacrylate, or a mixture thereof. More preferably, the unit (R N-2 ) is derived from 2-hydroxyethyl methacrylate (HEMA).

[0112] Also in some other embodiments, the unit (R N ) is derived from at least one monomer selected from the list consisting of: methyl methacrylate, ethyl methacrylate, butyl acrylate, methyl acrylate, ethyl acrylate, butyl acrylate, vinyl acetate, and N,N-dimethylacrylamide, [unit (R N-1 )] and at least one monomer selected from the list consisting of: 2-hydroxyethyl methacrylate (HEMA), hydroxypropyl methacrylate, 2-hydroxyethyl acrylate (HEA), hydroxypropyl acrylate, 4-hydroxybutyl acrylate, poly(ethylene glycol) methacrylate (PEGMA), poly(ethylene glycol) methyl ether methacrylate (mPEGMA), poly(ethylene glycol) ethyl ether methacrylate, poly(ethylene glycol) methyl ether acrylate, and poly(ethylene glycol) ethyl ether acrylate, [unit (R N-2 )]. Preferably, the unit (R N-1 ) is derived from methyl methacrylate, ethyl methacrylate, or a mixture thereof and the unit (R N-2 ) is derived from 2-hydroxyethyl methacrylate (HEMA), hydroxypropyl methacrylate, or a mixture thereof. More preferably, the unit (R N-1 ) is derived from methyl methacrylate and the unit (R N-2 ) is derived from 2-hydroxyethyl methacrylate (HEMA).

[0113] In some preferred embodiments, the copolymer (N-ZW) of the present disclosure comprises repeating units (R ZW ) derived from 2-(dimethylammonio)ethyl methacrylate sulfonate (SPE), 1-(3-sulfopropyl)-2-vinylpyridinium (2SPV), or a mixture thereof and repeating units (R N-1 ) derived from methyl methacrylate.

[0114] In some more preferred embodiments, the copolymer (N-ZW) of the present disclosure comprises repeating units (R ZW ) derived from 2-(methacryloyloxy)ethyl-dimethyl-(3-sulfopropyl)ammonium hydroxide (SPE) and repeating units (R N-1 ) derived from methyl methacrylate.

[0115] Also in some more preferred embodiments, the copolymer (N-ZW) of the present disclosure comprises repeating units (R ZW ) derived from (SPE) or (2SPV), repeating units (R N-1 ) derived from methyl methacrylate, and repeating units (R N-2 ) derived from 2-hydroxyethyl methacrylate (HEMA).

[0116] The copolymer (N-ZW) of the composition (C) according to the present disclosure generally comprises, based on the total molar amount of the repeating units of the copolymer (N-ZW), 80% or more, preferably 90% or more, more preferably 93% or more, and even more preferably 95% or more, by mole, of the units (R N ).

[0117] When the repeating units (R N-1 ) and the repeating units (R N-2 ) are present, the copolymer (N-ZW) generally comprises, based on the total molar amount of the repeating units of the copolymer (N-ZW), from 0.1% to 50%, preferably from 0.1% to 40%, more preferably from 0.1% to 30%, and even more preferably from 0.1% to 20%, by mole, of the repeating units (R ZW ) and (R N-2 ).

[0118] The copolymer (N-ZW) according to the present invention is a block copolymer, a branched copolymer or a statistical copolymer. Good results have been obtained in the case where the copolymer (N-ZW) is a statistical copolymer.

[0119] Unless otherwise specified, when referring to the molar mass, the weight-average molar mass expressed in g / mol will be meant. The latter can be determined by gel permeation chromatography (GPC) with light scattering detection (DLS or alternatively MALLS) or refractive index detection, using an aqueous eluent or an organic eluent (e.g., dimethylacetamide, dimethylformamide, etc.) (depending on the copolymer (N-ZW)). The weight-average molar mass (Mw) of the copolymer (N-ZW) ranges from 25,000 to 350,000 g / mol, typically from about 35,000 to about 300,000 g / mol, more typically from about 70,000 to 250,000 g / mol, and even more typically from 80,000 to 200,000 g / mol.

[0120] The copolymers (N-ZW) of the present disclosure can be obtained by any polymerization method known to those of ordinary skill in the art. For example, the copolymers (N-ZW) can be obtained by free radical polymerization or controlled free radical polymerization in an aqueous solution, a dispersion medium, an organic solution, or an organic / aqueous solution (miscible phase).

[0121] Monomers that can give rise to the unit (R N ) without ionizable groups are commercially available.

[0122] Zwitterionic monomers that give rise to the unit (R ZW ) are commercially available or can be synthesized according to methods known to those of ordinary skill in the art.

[0123] Suitable zwitterionic monomers that can give rise to the unit (R ZW ) include, but are not limited to, monomers selected from the list consisting of:

[0124] a) Dialkylammonium alkyl acrylates or methacrylates, alkyl or hydroxyalkyl sulfonates or phosphonates of acrylamido or methacrylamido, typically:

[0125] - Ethyl dimethylammonium sulfopropyl methacrylate sold by Raschig under the name MER SPE

[0126]

[0127] - Ethyl dimethylammonium sulfoethyl methacrylate,

[0128]

[0129] - Ethyl dimethylammonium sulfobutyl methacrylate:

[0130]

[0131] Its synthesis is described in the paper "Sulfobetaine zwitterionomers based on n-butyl acrylate and 2-ethoxyethyl acrylate: monomer synthesis and copolymerization behavior", Journal of Polymer Science, 40, 511-523 (2002).

[0132] -2-(Methacryloyloxy)ethyl dimethyl-(3-sulfopropyl)ammonium hydroxide

[0133]

[0134] and other hydroxyalkyl sulfonates of dialkylammonium alkyl acrylates or methacrylates, acrylamido or methacrylamido having the formula

[0135]

[0136] -3-(Methacrylamido)propyl dimethyl-(3-sulfopropyl)ammonium

[0137] Its synthesis is described in the paper "Synthesis and solubility of the poly(sulfobetaine)s and the corresponding cationic polymers: 1. Synthesis and characterization of sulfobetaines and the corresponding cationic monomers by nuclear magnetic resonance spectra", Wen-Fu Lee and Chan-Chang Tsai, Polymer, 35(10), 2210-2217 (1994).

[0138] -3-(Methacrylamido)propyl dimethyl-(3-sulfopropyl)ammonium sold by RASCHIG GmbH under the name SPP:

[0139]

[0140] -2-(Methacryloyloxy)ethyl diethyl-(3-sulfopropyl)ammonium hydroxide

[0141]

[0142] Its synthesis is described in the paper “Poly(sulphopropylbetaines): 1. Synthesis and characterization”, V.M. Monroy Soto and J.C. Galin, Polymer, 1984, Vol. 25, 121-128;

[0143] b) Heterocyclic betaine monomers, typically:

[0144] - Sulphobetaines derived from piperazine, these sulphobetaines having any of the following structures

[0145]

[0146]

[0147] Its synthesis is described in the paper “Hydrophobically Modified Zwitterionic Polymers: Synthesis, Bulk Properties, and Miscibility with Inorganic Salts”, P. Koberle and A. Laschewsky, Macromolecules, 27, 2165-2173 (1994),

[0148]

[0149]

[0150] - Sulphobetaines derived from 2-vinylpyridine and 4-vinylpyridine, such as 2-vinyl-1-(3-sulphopropyl)pyridinium betaine (2SPV), sold by Raschig GmbH under the name SPV:

[0151]

[0152] and 4-vinyl-1-(3-sulphopropyl)pyridinium betaine (4SPV),

[0153]

[0154] Its synthesis is disclosed in the paper "Evidence of ionic aggregates in some ampholytic polymers by transmission electron microscopy", V.M. and A.E. González, J. Cardoso, O. Manero and V.M. Monroy, J. Mater. Res., 5(3), 654 - 657 (1990), and other hydroxyalkyl sulfonates derived from 2 - vinylpyridine and 4 - vinylpyridine having the formula

[0155]

[0156] -1 - vinyl - 3-(3 - sulfopropyl)imidazolium betaine:

[0157]

[0158] Its synthesis is described in the paper "Aqueous solution properties of a poly(vinyl imidazolium sulfobetaine)", J.C. Salamone, W. Volkson, A.P. Oison, S.C. Israel, Polymer, 19, 1157 - 1162 (1978), and the corresponding hydroxyalkyl sulfonates having the formula

[0159]

[0160] c) Alkyl or hydroxyalkyl sulfonates or phosphonates of dialkylammonium alkyl allyls, typically sulfopropyl methyldiallylammonium betaine:

[0161]

[0162] Its synthesis is described in the paper "New poly(carbobetaine)s made from zwitterionic diallylammonium monomers", Favresse, Philippe; Laschewsky, Andre, Macromolecular Chemistry and Physics, 200(4), 887 - 895 (1999),

[0163] d) Alkyl or hydroxyalkyl sulfonates or phosphonates of dialkylammonium alkylstyrenes, typically compounds having any of the following structures:

[0164]

[0165] The synthesis of which is described in the paper "Hydrophobically Modified Zwitterionic Polymers: Synthesis, Bulk Properties, and Miscibility with Inorganic Salts", P. Koberle and A. Laschewsky, Macromolecules, 27, 2165 - 2173 (1994), and other hydroxyalkyl sulfonates of dialkylammonium alkylstyrenes having the following formula

[0166]

[0167] e) Betaines produced from ethylenically unsaturated acid anhydrides and dienes, typically compounds having any of the following structures:

[0168]

[0169] The synthesis of which is described in the paper "Hydrophobically Modified Zwitterionic Polymers: Synthesis, Bulk Properties, and Miscibility with Inorganic Salts", P. Koberle and A. Laschewsky, Macromolecules, 27, 2165 - 2173 (1994),

[0170] f) Phosphatobetaines having any of the following structures:

[0171]

[0172] The synthesis of which is disclosed in EP 810 239B1 (Biocompatibles Corporation, Alister et al.);

[0173] g) Betaines produced from cyclic acetals, typically ((dicyanoethanolate)ethoxy)dimethylammonium propylmethacrylamide:

[0174]

[0175] Its synthesis is described in the paper by M-L. Pujol-Fortin et al., titled "Poly(ammonium alkoxydicyanatoethenolates) as new hydrophobic and highly dipolar poly(zwitterions). 1. Synthesis", Macromolecules, 24, 4523-4530 (1991).

[0176] Suitable monomers containing a hydroxyalkyl sulfonate moiety that can give rise to the unit (R ZW ) can be obtained by the reaction of sodium 3-chloro-2-hydroxypropane-1-sulfonate (CHPSNa) with monomers bearing a tertiary amino group, as described for the synthesis of SHPP in US20080045420, starting from dimethylaminopropyl methacrylamide according to the reaction scheme:

[0177]

[0178] Other monomers bearing a tertiary amino group can participate in the reaction with CHPSNa to obtain suitable monomers that give rise to the unit (R ZW ):

[0179]

[0180] Suitable monomers that give rise to the unit (R ZW ) can also be obtained by the reaction of sodium 3-chloro-2-hydroxypropane-1-sulfonate (CHPSNa) with monomers bearing a pyridine or imidazole group:

[0181]

[0182] The expression "derived from" that links the repeating unit (R ZW ) to the monomer is intended to define both the repeating unit (R ZW ) obtained directly from the polymerization of the monomer and the same repeating unit (R ZW ) obtained by modification of an existing polymer.

[0183] Thus, the repeating unit (R ZW) It can be obtained by modifying a polymer containing repeating units with a tertiary amino group (referred to as a precursor polymer) via reaction with sodium 3-chloro-2-hydroxypropane-1-sulfonate (CHPSNa). A similar modification is described in WO 2008125512, using sodium 3-chloropropane-1-sulfonate instead of CHPSNa:

[0184]

[0185] Finally, the repeating unit (R ZW ) can be obtained by chemically modifying a polymer (referred to as a precursor polymer) with a sultone (such as propane sultone or butane sultone), a haloalkyl sulfonate ester, or any other sulfonated electrophilic compound known to those of ordinary skill in the art. Exemplary synthesis steps are shown below:

[0186]

[0187] Similarly, the repeating unit (R ZW ) can be obtained by modifying a polymer (referred to as a precursor polymer) containing repeating units with a tertiary amino group, a pyridyl group, an imidazolyl group, or a mixture thereof via reaction with sodium 3-chloro-2-hydroxypropane-1-sulfonate (CHPSNa), a sultone (such as propane sultone or butane sultone), or a haloalkyl sulfonate ester.

[0188] Since the copolymer (N-ZW) is used as an additive to the polymer (VDF), in the composition (C), the polymer (VDF) is typically present in a significant amount relative to the copolymer (N-ZW). Typically, the weight ratio of copolymer (N-ZW) / polymer (VDF) is at least 0.1 / 99.9 wt / wt, preferably at least 1 / 99 wt / wt, more preferably at least 3 / 97 wt / wt and / or less than 25 / 75 wt / wt, preferably less than 20 / 80 wt / wt, more preferably less than 15 / 85 wt / wt, and even more preferably less than 10 / 90 wt / wt.

[0189] The composition (C) may optionally contain at least one additional component. The additional component is preferably selected from the group consisting of: non-solvents (water, alcohols...), co-solvents (such as ketones), pore formers, nucleating agents, fillers, salts, surfactants.

[0190] When used, a pore former is typically added to the composition (C) in an amount ranging generally from 1% to 30% by weight, preferably from 2% to 20% by weight, based on the total weight of the composition (C). Suitable pore formers are, for example, polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), and polyethylene glycol (PEG).

[0191] Liquid medium

[0192] In some embodiments, the composition (C) further comprises at least one liquid medium [medium (L)], the at least one liquid medium comprising at least one organic solvent, [composition (C L )].

[0193] The term "solvent" is used herein in its usual meaning, i.e., it denotes a substance capable of dissolving another substance (solute) to form a mixture that is homogeneously dispersed at the molecular level. In the case of a polymeric solute, the convention is that a solution of the polymer in the solvent is meant when the resulting mixture is transparent and there is no visible phase separation in the system. The point at which phase separation occurs, commonly referred to as the "cloud point", is considered to be the point at which the solution becomes cloudy or turbid due to the formation of polymer aggregates.

[0194] Generally, in the composition (C L ), the medium (L) comprises at least one solvent (S) for the polymer (VDF).

[0195] The medium (L) typically comprises at least one organic solvent selected from the group consisting of:

[0196] - aliphatic hydrocarbons, including more specifically paraffins such as especially pentane, hexane, heptane, octane, nonane, decane, undecane, dodecane or cyclohexane, and naphthalene and aromatic hydrocarbons and more specifically aromatic hydrocarbons such as especially benzene, toluene, xylene, cumene, petroleum fractions consisting of mixtures of alkylbenzenes;

[0197] - aliphatic or aromatic halogenated hydrocarbons, including more specifically perchlorinated hydrocarbons such as especially tetrachloroethylene, hexachloroethane;

[0198] - partially chlorinated hydrocarbons such as dichloromethane, chloroform, 1,2-dichloroethane, 1,1,1-trichloroethane, 1,1,2,2-tetrachloroethane, pentachloroethane, trichloroethylene, 1-chlorobutane, 1,2-dichlorobutane, monochlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,2,4-trichlorobenzene or mixtures of different chlorobenzenes;

[0199] - aliphatic, cycloaliphatic or aromatic ether oxides, more specifically, diethyl oxide, dipropyl oxide, diisopropyl oxide, dibutyl oxide, methyl tert-butyl ether, dipentyl oxide, diisopentyl oxide, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether benzyl oxide; dioxane, tetrahydrofuran (THF);

[0200] - dimethyl sulfoxide (DMSO);

[0201] - Glycol ethers, such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monophenyl ether, ethylene glycol monobenzyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monon-butyl ether;

[0202] - Glycol ether esters, such as ethylene glycol methyl ether acetate, ethylene glycol monoethyl ether acetate, ethylene glycol monobutyl ether acetate;

[0203] - Alcohols, including polyols, such as methanol, ethanol, diacetone alcohol, ethylene glycol;

[0204] - Ketones, such as acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone, isophorone;

[0205] - Linear or cyclic esters, such as isopropyl acetate, n-butyl acetate, methyl acetoacetate, dimethyl phthalate, γ-butyrolactone;

[0206] - Linear or cyclic carboxamides, such as N,N-dimethylacetamide (DMAc), N,N-diethylacetamide, dimethylformamide (DMF), diethylformamide or N-methyl-2-pyrrolidone (NMP);

[0207] - Organic carbonates, such as dimethyl carbonate, diethyl carbonate, dipropyl carbonate, dibutyl carbonate, ethyl methyl carbonate, ethylene carbonate, vinylene carbonate;

[0208] - Phosphoric esters, such as trimethyl phosphate, triethyl phosphate (TEP);

[0209] - Ureas, such as tetramethylurea, tetraethylurea;

[0210] - Methyl 5-dimethylamino-2-methyl-5-oxopentanoate (commercially available under the trade name Rhodialsov and available commercially).

[0211] The following are preferred: linear or cyclic carboxamides, such as N,N-dimethylacetamide (DMAc), N,N-diethylacetamide, dimethylformamide (DMF), diethylformamide or N-methyl-2-pyrrolidone (NMP), dimethyl sulfoxide (DMSO), tetrahydrofuran (THF), methyl 5-dimethylamino-2-methyl-5-oxopentanoate (commercially available under the trade name Rhodialsov and available commercially) and triethyl phosphate (TEP).

[0212] Linear or cyclic carboxamides, such as N,N-dimethylacetamide (DMAc), N,N-diethylacetamide, dimethylformamide (DMF), diethylformamide or N-methyl-2-pyrrolidone (NMP) are particularly preferred.

[0213] N-methyl-pyrrolidone (NMP) and dimethylacetamide (DMAc) are even more preferred.

[0214] The medium (L) may further comprise at least one additional liquid component (or in other words, non-solvent) different from the solvent (S).

[0215] The additional liquid component that does not have the ability to dissolve the polymer (VDF) can be added to the composition (C L ), and the amount is usually below the level required to reach the cloud point, typically in an amount of from 0.1% to 40% by weight, preferably from 0.1% to 20% by weight, based on the total weight of the medium (L) of the composition (C L ). Without being bound by this theory, it is generally understood that adding a non-solvent to the composition (C L ) may be advantageously beneficial in increasing the rate of phase separation / coagulation during the manufacture of the porous membrane and / or promoting solidification by removing the solvent (S) by evaporation.

[0216] Generally, the composition (C L ) comprises a total amount of the copolymer (N-ZW) and the polymer (VDF) of at least 1 wt.%, more preferably at least 3 wt.%, even more preferably at least 5 wt.%, based on the total weight of the medium (L), the copolymer (N-ZW), and the polymer (VDF), and / or the composition (C L ) preferably comprises a total amount of the copolymer (N-ZW) and the polymer (VDF) of at most 60 wt.%, more preferably at most 50 wt.%, even more preferably at most 30 wt.%, based on the total weight of the medium (L), the copolymer (N-ZW), the polymer (VDF), and / or the composition (C L ).

[0217] Conversely, the amount of the medium (L) in the composition (C L ) is at least 40 wt.%, preferably at least 50 wt.%, even more preferably at least 70 wt.%, based on the total weight of the medium (L), the copolymer (N-ZW), and the polymer (VDF), and / or the amount of the medium (L) in the composition (C L ) is at most 99 wt.%, preferably at most 97 wt.%, even more preferably at most 95 wt.%, based on the total weight of the medium (L), the copolymer (N-ZW), and the polymer (VDF).

[0218] The composition (C L ) may optionally comprise at least one additional ingredient. The additional ingredient is preferably selected from the group consisting of: pore former, nucleating agent, filler, salt, surfactant.

[0219] When used, typically to the composition (CL ) A pore former is added thereto, and the amount thereof generally ranges from 0.1% to 30% by weight, preferably from 0.5% to 20% by weight, based on the total weight of the composition (C L ). Suitable pore formers are, for example, polyvinyl alcohol (PVA), cellulose acetate, polyvinylpyrrolidone (PVP), and polyethylene glycol (PEG).

[0220] Method for manufacturing a porous membrane

[0221] A second aspect of the present invention relates to a method for manufacturing a porous membrane, the method comprising:

[0222] Step (i): preparing a composition (C L ) as defined above;

[0223] Step (ii): processing the composition provided in step (i) to provide a thin film; and,

[0224] Step (iii): processing the thin film provided in step (ii), generally comprising contacting the thin film with a non-solvent medium [medium (NS)] to provide a porous membrane.

[0225] In step (i), the composition (C L ) is manufactured by any conventional technique. For example, the medium (L) can be added to the polymer (VDF) and the copolymer (N-ZW), or preferably, the polymer (VDF) and the copolymer (N-ZW) are added to the medium (L), or even the polymer (VDF), the copolymer (N-ZW), and the medium (L) are mixed simultaneously.

[0226] Any suitable mixing device can be used. Preferably, the mixing device is selected to reduce the amount of air entrained in the composition (C L ), and such entrainment may cause defects in the final membrane. The mixing of the polymer (VDF), the copolymer (N-ZW), and the medium (L) can be conveniently carried out in a sealed container, optionally maintained under an inert atmosphere. It has been found that an inert atmosphere and more precisely a nitrogen atmosphere are particularly advantageous for manufacturing the composition (C L ).

[0227] In step (i), the mixing time and stirring rate required to obtain a clear and homogeneous composition (C L ) can vary widely depending on the dissolution rate of the components, temperature, efficiency of the mixing device, viscosity of the composition (C L ), etc.

[0228] In step (ii) of the method of the present invention, conventional techniques can be used to process the composition (C L ) to provide a thin film.

[0229] In step (ii), the composition (C) is typically processed by casting L ) to provide a film.

[0230] Casting typically involves solution casting, where the composition (C) L ) is typically spread as a uniform film onto a suitable support using a casting knife, draw bar, or slot die.

[0231] In step (ii), the temperature at which the composition (C) L ) is processed by casting can be the same as or different from the temperature at which the composition (C) L ) is mixed under agitation.

[0232] Depending on the final form of the film to be produced, different casting techniques are used.

[0233] When the final product is a flat film, the composition (C) L ) is typically cast as a film onto a flat support substrate (typically a floor, belt, or fabric) or another microporous support membrane using a casting knife, draw bar, or slot die.

[0234] According to a first embodiment of step (ii), the composition (C) L ) is processed by casting onto a flat support substrate to provide a flat film.

[0235] According to a second embodiment of step (ii), the composition (C) L ) is processed by casting to provide a tubular film.

[0236] According to a variant of this second embodiment of the invention, a spinneret is used to produce the tubular film, a technique which is additionally commonly referred to as the "spinning method". Hollow fibers and capillary membranes can be produced according to the spinning method.

[0237] The term "spinneret" is hereby to be understood to mean an annular nozzle comprising at least two concentric capillaries: a first outer capillary through which the composition (C) L ) passes and a second inner capillary (commonly referred to as the "lumen") through which a support fluid (also referred to as the "hole fluid") passes.

[0238] According to this variant of the second embodiment, the composition (C) L ) is typically pumped through the spinneret together with at least one support fluid (the so-called "hole fluid"). The support fluid serves to cast the composition (C) L) The support functions to keep the pores of the hollow fiber or capillary precursor open. The support fluid can be a gas, or preferably a non-solvent medium [medium (NS)] or a mixture of medium (NS) and medium (L). The choice of the support fluid and its temperature depends on the desired properties of the final membrane, as they can have a significant impact on the size and distribution of the pores in the membrane.

[0239] Step (iii) generally includes the step of contacting the thin film provided in step (ii) with a non-solvent medium [medium (NS)], thereby providing a porous membrane.

[0240] This step of contacting with medium (NS) typically effectively precipitates and solidifies the composition (C L ) that constitutes the thin film in step (ii) into a porous membrane.

[0241] The thin film can be precipitated in the medium (NS) by immersion in a bath of medium (NS), which is typically referred to as a coagulation bath.

[0242] As an alternative (or typically before immersion in the coagulation bath), contacting the thin film with medium (NS) can be achieved by exposing the thin film to a gas phase containing the vapor of the medium (NS).

[0243] Typically, the gas phase is prepared, for example, by at least partially saturating with the vapor of medium (NS), and the thin film is exposed to the gas phase. For example, air with a relative humidity higher than 10%, typically higher than 50% (i.e., containing water vapor) can be used.

[0244] Before contacting with the non-solvent medium (by any of the techniques explained above), the thin film can be exposed to air and / or a controlled atmosphere for a given residence time in the substantial absence of the medium (NS). This additional step may be beneficial for forming an epidermis on the exposed surface of the thin film by an alternative mechanism.

[0245] For example, in a spinning method, this can be achieved by applying an air gap in the path along which the spun hollow tubular precursor travels before entering the coagulation bath.

[0246] According to certain embodiments, in step (iii), the coagulation / precipitation of the composition (C L ) can be promoted by cooling. In this case, the cooling of the thin film provided in step (ii) can typically be carried out using any conventional technique.

[0247] Generally, when heat-induced coagulation / precipitation occurs, the composition (C L) The solvent (S) of the medium (L) is advantageously a "latent" solvent [solvent (LT)], i.e., a solvent that is only active towards the polymer (VDF) when heated above a certain temperature and cannot dissolve the polymer (VDF) below said temperature.

[0248] When the medium (L) contains a latent solvent or solvent (LT), steps (i) and (ii) of the method of the present invention are generally carried out at a temperature high enough to keep the composition (C L ) as a homogeneous solution.

[0249] For example, in step (ii), according to this embodiment, the film can typically be processed at a temperature between 60 °C and 250 °C, preferably between 70 °C and 220 °C, more preferably between 80 °C and 200 °C, and in step (iii), the film can typically be precipitated by cooling to a temperature below 100 °C, preferably below 60 °C, more preferably below 40 °C.

[0250] Cooling can be achieved by bringing the film provided in step (ii) into contact with a cooling fluid, which can be a gaseous fluid (i.e., cooled air or a cooled modified atmosphere) or can be a liquid fluid.

[0251] In the latter case, the medium (NS) detailed above is typically used so that the phenomena of non-solvent-induced and heat-induced precipitation can occur simultaneously.

[0252] However, it should generally be understood that even in cases where heat-induced precipitation occurs, an additional step of contacting with the medium (NS) is carried out, for example, to complete the precipitation and facilitate the removal of the medium (L).

[0253] In cases where the medium (L) contains both a solvent (S) and a non-solvent for the polymer (VDF), at least partial selective evaporation of the solvent (S) can be used to promote the solidification / precipitation of the polymer (VDF). In this case, the solvent (S) and non-solvent components of the medium (L) are typically selected so as to ensure that the solvent (S) has a higher volatility than the non-solvent, such that the solvent (S) is typically evaporated step by step under controlled conditions, causing the polymer (VDF) to precipitate and thus the actual contact of the film with the medium (NS).

[0254] When present in the composition (C L ) in step (iii) of the method of the present invention, the pore former is generally at least partially (if not completely) removed from the porous film in the medium (NS).

[0255] In all these methods, it should generally be understood that the temperature gradients during steps (ii) and (iii), the properties of the media (NS) and (L), including the presence of non-solvents in the medium (L), are parameters known to those skilled in the art for controlling the morphology (including its average porosity) of the final porous membrane.

[0256] The method of the present invention may include additional post-treatment steps, such as steps of rinsing and / or stretching the porous membrane and / or drying the porous membrane.

[0257] For example, the porous membrane may alternatively be rinsed with a liquid medium miscible with the medium (L).

[0258] Furthermore, the porous membrane may be advantageously stretched to increase its average porosity.

[0259] Typically, the porous membrane is dried at a temperature of at least 30 °C advantageously.

[0260] Drying may be carried out in air or in a modified atmosphere, such as in an inert gas, typically removing moisture (water vapor content less than 0.001% v / v). Drying may alternatively be carried out under vacuum.

[0261] For the purposes of the present invention, the term "non-solvent medium [medium (NS)]" means a medium composed of one or more liquid substances that cannot dissolve the composition (C) or the polymer (VDF) of (C L ) and that advantageously promotes the solidification / precipitation of the polymer (VDF) from the liquid medium of the composition (C L ).

[0262] The medium (NS) typically comprises water and optionally at least one organic solvent selected from alcohols or polyols, which organic solvent is preferably a fatty alcohol having a short chain, for example from 1 to 6 carbon atoms, more preferably methanol, ethanol, isopropanol and ethylene glycol.

[0263] The medium (NS) is generally selected from those that are miscible with the medium (L) used for preparing the composition (C L ).

[0264] The medium (NS) may further comprise the solvent (S) as detailed above.

[0265] More preferably, the medium (NS) consists of water. Water is the cheapest non-solvent medium and can be used in large quantities.

[0266] Porous membrane

[0267] The third aspect of the present invention relates to a porous membrane comprising:

[0268] - at least one vinylidene fluoride polymer [polymer (VDF)], and

[0269] - at least one copolymer [copolymer (N-ZW)], which comprises

[0270] (a) repeating units [units (R ZW )] derived from at least one zwitterionic monomer [monomer (A)], and

[0271] (b) repeating units [units (R N )] derived from at least one additional monomer [monomer (B)] different from monomer (A),

[0272] where, based on the molar composition of the copolymer (N-ZW), the units (R ZW ) account for 0.1 to 7 mol%, preferably 0.1 to 5 mol%, and

[0273] where the molecular weight of the copolymer (N-ZW) measured by gel permeation chromatography ranges from 25,000 g / mol to 350,000 g / mol, and

[0274] where the weight ratio copolymer (N-ZW) / polymer (VDF) is at least 0.1 / 99.9 and / or less than 25 / 75.

[0275] The expression "porous membrane" is used according to its ordinary meaning in the art, i.e., it denotes a membrane that includes pores (i.e., voids or cavities) of any shape and size.

[0276] As mentioned, the porous membrane of the present invention is obtainable from the composition (C L ) detailed above and / or is manufactured using the method detailed above.

[0277] The porous membrane of the present invention can be in the form of a flat membrane or in the form of a tubular membrane.

[0278] When high throughput is required, flat membranes are generally preferred, while in applications where a compact module with a high surface area is required, hollow fiber membranes are particularly advantageous.

[0279] The flat membrane preferably has a thickness comprised between 10 μm and 200 μm, more preferably between 15 μm and 150 μm.

[0280] The tubular membrane typically has an outer diameter greater than 3 mm. A tubular membrane having an outer diameter comprised between 0.5 mm and 3 mm is typically referred to as a hollow fiber membrane. A tubular membrane having a diameter less than 0.5 mm is typically referred to as a capillary membrane.

[0281] A membrane containing pores with a uniform distribution throughout its thickness is generally referred to as a symmetric (or isotropic) membrane; a membrane containing pores with a non-uniform distribution throughout its thickness is generally referred to as an asymmetric (or anisotropic) membrane.

[0282] The porous membrane according to the present invention can be a symmetric membrane or an asymmetric membrane.

[0283] An asymmetric porous membrane typically consists of one or more layers containing pores with a non-uniform distribution throughout their thickness.

[0284] An asymmetric porous membrane typically includes an outer layer containing pores having an average pore diameter smaller than the average pore diameter of the pores in one or more inner layers.

[0285] The porous membrane of the present invention preferably has an average pore diameter of at least 0.001 μm, more preferably at least 0.005 μm, and even more preferably at least 0.01 μm. The porous membrane of the present invention preferably has an average pore diameter of at most 50 μm, more preferably at most 20 μm, and even more preferably at most 15 μm.

[0286] Suitable techniques for determining the average pore diameter in the porous membrane of the present invention are described, for example, in Handbook of Industrial Membrane Technology, edited by PORTER, Mark C., Noyes Publications, 1990, pages 70 - 78.

[0287] The porous membrane of the present invention typically has a weight porosity, by volume based on the total volume of the membrane, of between 5% and 90%, preferably between 10% and 85%, and more preferably between 30% and 90%.

[0288] For the purposes of the present invention, the term "weight porosity" is intended to represent the fraction of voids relative to the total volume of the porous membrane.

[0289] Suitable techniques for determining the weight porosity in the porous membrane of the present invention are described, for example, in Terminology for membrane distillation by SMOLDERS, K., et al., Desalination, 1989, Volume 72, pages 249 - 262.

[0290] The porous membrane of the present invention can be a self - standing porous membrane or a porous membrane supported on a substrate and / or containing a backing layer.

[0291] The porous membrane includes at least one layer containing at least one polymer (VDF) and at least one copolymer (N - ZW).

[0292] A porous membrane supported on a substrate can typically be obtained by laminating the substrate and / or backing with a pre-formed porous membrane or by fabricating the porous membrane directly on the substrate and / or the backing.

[0293] Thus, the porous membrane can be composed of a single layer containing polymer (VDF) and copolymer (N-ZW) or can include additional layers.

[0294] In particular, the porous membrane of the present invention can further comprise at least one substrate. The substrate can be partially or completely interpenetrated by the porous membrane of the present invention.

[0295] The nature of the substrate / backing is not particularly limited. The substrate is generally composed of a material that has a minimal impact on the selectivity of the porous membrane. The substrate layer is preferably composed of non-woven materials, polymer materials (such as polypropylene), glass, and glass fibers.

[0296] In some embodiments, the porous membrane of the present invention is a porous composite membrane assembly, which comprises:

[0297] - at least one substrate layer, preferably a non-woven substrate,

[0298] - at least one top layer, and

[0299] - between the at least one substrate layer and the at least one top layer, at least one layer containing at least one polymer (VDF) and at least one copolymer (N-ZW).

[0300] Typical examples of such porous composite membrane assemblies are so-called thin film composite (TFC) structures, which are typically used in reverse osmosis or nanofiltration applications.

[0301] Non-limiting examples of top layers suitable for the porous composite membrane assemblies of the present invention include those made of polymers selected from the group consisting of: polyamide, polyimide, polyacrylonitrile, polybenzimidazole, cellulose acetate, and polyolefin.

[0302] The porous membrane layer containing polymer (VDF) and copolymer (N-ZW) can additionally contain one or more additional components. However, embodiments in which the porous membrane includes at least one layer mainly composed of polymer (VDF) and copolymer (N-ZW) are preferred, it being understood that residues of additives and / or pore formers can be present in an amount not exceeding 5 wt.% of the layer.

[0303] In the porous membrane, the copolymer (N-ZW) is used as an additive to the polymer (VDF), so it is generally understood that the polymer (VDF) is present in a significant amount relative to the copolymer (N-ZW). Generally, the weight ratio of copolymer (N-ZW) / polymer (VDF) is at least 0.1 / 99.9 wt / wt, preferably at least 1 / 99 wt / wt, more preferably at least 3 / 97 wt / wt and / or less than 50 / 50 wt / wt, preferably less than 40 / 60 wt / wt, preferably less than 30 / 70 wt / wt.

[0304] Method for separating an aqueous medium

[0305] A fourth aspect of the present invention relates to a method for separating an aqueous medium, the method comprising contacting the aqueous medium with the porous membrane as described above.

[0306] All of the features described above with respect to the porous membrane of the present invention apply to its use in the method described herein.

[0307] Depending on its average pore size, the porous membrane of the present invention has different uses and can be applied to various separation processes, such as microfiltration, ultrafiltration, reverse osmosis, which vary greatly in terms of the size of the "rejected" / rejected entities, which can be of any nature.

[0308] The expression "aqueous medium" is not particularly limited and encompasses all media including water, including biological fluids, natural fluids or synthetic mixtures.

[0309] The method for separating an aqueous medium of the present invention can be particularly applied to the desalination of brackish water and seawater, wastewater treatment / recovery, can be used in the food industry, and can ultimately be used for the separation and purification of chemical and biological products.

[0310] According to certain embodiments, the aqueous phase can in particular be a water-based phase containing one or more contaminants.

[0311] The aqueous phase can be a particulate suspension of contaminants, i.e., a suspension containing chemical or physical contaminants (e.g., inorganic particles such as sand, grit, metal particles, ceramics; organic solids such as polymers, paper fibers, plant and animal residues; biological contaminants such as bacteria, viruses, protozoa, parasites).

[0312] The separation method of the present invention can be used to filter biological solutions (e.g., bioburden, viruses, other macromolecules) and / or buffer solutions (e.g., solutions that may contain small amounts of solvents (such as DMSO) or other polar aprotic solvents).

[0313] For example, the separation method of the present invention can be a method for purifying biological fluids, such as in particular blood, especially in an extracorporeal blood circuit or a dialysis filter. In this case, the porous membrane used generally has an average pore size ranging from 0.001 to 5 μm and can be in the form of a tubular or hollow fiber membrane.

[0314] In addition, the separation method of the present invention can be in particular a method for filtering a water suspension from suspended particles; in this case, the porous membrane used generally has an average pore size ranging from 5 μm to 50 μm.

[0315] The present invention will now be described in conjunction with the following examples, the scope of which is merely illustrative and not intended to limit the scope of the present invention.

[0316] Experiment

[0317] Raw materials

[0318] PVDF provided by Solvay Specialty Polymers 1015 was used as a VDF homopolymer.

[0319] The following solvent reactants and solvents were obtained from Sigma Aldrich: and used as received: 2,2'-azobis(2-methylbutyronitrile) (AMBN), methyl methacrylate (MMA), 3-((2-(methacryloyloxy)ethyl)dimethylammonio)propane-1-sulfonate also known as N,N-dimethyl-N-(2-methacryloyloxyethyl)-N-(3-sulfopropyl)ammonium betaine (SPE), 3-(2-vinylpyridin-1-ium-yl)propane-1-sulfonate (2SPV), dimethyl sulfoxide (DMSO), N,N-dimethylacetamide (DMAc), and N-methyl-2-pyrrolidone (NMP).

[0320] Molecular weight determination

[0321] Gel permeation chromatography was carried out at 40 °C using a Jasco PU-2080Plus HPLC pump equipped with 2 SHODEX KD-804 columns and a Jasco Refractiveindex-4030 detector. The mobile phase consisted of 1.5% LiBr in DMF and the flow rate was 1.0 mL / min. 100 μL of the sample (concentration of about 5.0 mg / mL) was injected and calibrated with PMMA narrow standards.

[0322] Synthesis of poly(MMA-stat-SPE) 95 / 5 mol / mol (MW = 69000 g / mol)

[0323] In a 500 mL autoclave reactor equipped with a water condenser and mechanical stirring, at room temperature (22 °C), 75 g (187.30 mmol) of methyl methacrylate (MMA) solution (25 wt% in DMSO), 92.5 g of dimethyl sulfoxide (DMSO, 99% purity) and 55.1 g (9.5 mmol) of 3-((2-(methacryloyloxy)ethyl)dimethylammonio)propane-1-sulfonate (SPE) solution (5% in DMSO) were introduced. The mixture was degassed by nitrogen bubbling for 50 minutes while raising the temperature of the reaction medium to 70 °C. Then, 15.16 g (1.5 mmol) of AMBN solution (2% in DMSO) was introduced under a nitrogen layer. The reaction was carried out at 70 °C with stirring for 10 hours.

[0324] After that, a sample was taken for 1 1H NMR analysis to determine the MMA and SPE conversion rates. Results: MMA monomer conversion rate = 98.1%; SPE monomer conversion rate = 94.1%.

[0325] M W = 69000 g / mol.

[0326] Synthesis of poly(MMA-stat-SPE) 95 / 5 mol / mol (MW = 155400 g / mol)

[0327] In a 250 mL three-necked round-bottom flask equipped with a water condenser and mechanical stirring, at room temperature (22 °C), 92.42 g (261.2 mmol) of methyl methacrylate (MMA) solution (28.6 wt% in DMSO), 33 g of dimethyl sulfoxide (DMSO) and 15.12 g (13.7 mmol) of N,N-dimethyl-N-(2-methacryloyloxyethyl)-N-(3-sulfopropyl)ammonium betaine solution in water (27.2 wt%) were introduced. The mixture was degassed by nitrogen bubbling for 60 minutes while raising the temperature of the reaction medium to 70 °C. 1.8 g (1 mmol) of AIBN solution (10 wt% in DMSO) was further introduced under a nitrogen layer. Then, the reaction medium was stirred at 70 °C for 6 hours.

[0328] After polymerization, a sample was taken for 1 1H NMR analysis to determine the MMA and SPE conversion rates.

[0329] Results: MMA monomer conversion rate = 97%, SPE monomer conversion rate = 89%.

[0330] M W = 155400 g / mol

[0331] Synthesis of poly(MMA-stat-SPE) 90 / 10 mol / mol (Mw = 74800)

[0332] In a 6000 mL autoclave reactor equipped with a water condenser and mechanical stirring, at room temperature (22 °C), 450 g (4.45 mol) of methyl methacrylate (MMA, 99% purity), 5016.2 g of dimethyl sulfoxide (DMSO, 99% purity), and a solution of 142.38 g (0.49 mol) of 3-((2-(methacryloyloxy)ethyl)dimethylammonio)propane-1-sulfonate (SPE, 97% purity) in 265.6 g of distilled water were introduced. The mixture was degassed by bubbling nitrogen for 50 minutes while raising the temperature of the reaction medium to 70 °C. Then, 38.02 g (0.035 mol) of an AMBN solution (20% in DMSO) was introduced under a nitrogen blanket. The reaction was carried out at 70 °C with stirring for 10 hours.

[0333] After that, samples were taken for 1 1H NMR analysis to determine the MMA and SPE conversions. Results: MMA monomer conversion = 98.1%; SPE monomer conversion = 94.1%.

[0334] M W = 74800

[0335] Synthesis of poly(MMA-stat-SPE) 90 / 10 mol / mol (Mw = 144900)

[0336] In a 250 mL three-necked round-bottom flask equipped with a water condenser and mechanical stirring, at room temperature (22 °C), 133.13 g (228.7 mmol) of a methyl methacrylate (MMA) solution (17.4 wt% in DMSO), 31.9 g of dimethyl sulfoxide (DMSO), and a solution of 22.62 g (25.4 mmol) of N,N-dimethyl-N-(2-methacryloyloxyethyl)-N-(3-sulfopropyl)ammonium betaine in water (33.7 wt%) were introduced. The mixture was degassed by bubbling nitrogen for 60 minutes while raising the temperature of the reaction medium to 70 °C. Further, 0.83 g (1 mmol) of an AIBN solution (10 wt% in DMSO) was introduced under a nitrogen blanket. Then, the reaction medium was stirred at 70 °C for 24 hours.

[0337] After polymerization, samples were taken for 1 1H NMR analysis to determine the MMA and SPE conversions.

[0338] Results: MMA monomer conversion = 97%, SPE monomer conversion = 96%.

[0339] M W= 144900 g / mol

[0340] Synthesis of poly(MMA-stat-2SPV) 95 / 5 mol / mol (MW = 45000 g / mol)

[0341] In a 500 mL autoclave reactor equipped with a water condenser and mechanical stirring, at room temperature (22 °C), 75 g (187.30 mmol) of methyl methacrylate (MMA) solution (25 wt% in DMSO), 140.03 g of dimethyl sulfoxide (DMSO, 99% purity), and 6.4 g (9.3 mmol) of 3-(2-vinylpyridin-1-ium-yl)propane-1-sulfonate (2SPV) solution (35% in DMSO / H2O 80 / 20 w / w) were introduced. The mixture was degassed by nitrogen bubbling for 50 minutes while raising the temperature of the reaction medium to 70 °C. Then, 15.16 g (1.5 mmol) of AMBN solution (2% in DMSO) was introduced under a nitrogen layer. The reaction was carried out at 70 °C with stirring for 21 hours.

[0342] After that, samples were taken for 1 1H NMR analysis to determine the conversions of MMA and 2SPV. Results: MMA monomer conversion = 96.0%; 2SPV monomer conversion = 100%.

[0343] M W = 45000 g / mol

[0344] Similar experiments were carried out using a reduced amount of AMBN solution (i.e., a higher monomer / initiator ratio) to obtain a higher molecular weight.

[0345] Synthesis of poly(MMA-stat-2SPV) 90 / 10 mol / mol (Mw = 42600 g / mol)

[0346] In a 500 mL autoclave reactor equipped with a water condenser and mechanical stirring, at room temperature (22 °C), 75 g (187.30 mmol) of methyl methacrylate (MMA) solution (25 wt% in DMSO) and 140.03 g of dimethyl sulfoxide (DMSO, 99% purity) were introduced. The mixture was degassed by nitrogen bubbling for 50 minutes while raising the temperature of the reaction medium to 70 °C. Then, 16 g (1.5 mmol) of AMBN solution (2% in DMSO) was introduced under a nitrogen layer and 13.51 g (19.6 mmol) of 3-(2-vinylpyridin-1-ium-yl)propane-1-sulfonate (2SPV) solution (35% in DMSO / H2O 80 / 20 w / w) was added over 7 hours (flow rate of 0.03 g / min). The reaction was carried out at 70 °C with stirring for 22 hours.

[0347] After that, a sample was taken for 1 1H NMR analysis to determine the conversions of MMA and 2SPV. Results: MMA monomer conversion = 92.2%; 2SPV monomer conversion = 87.8%.

[0348] M W = 42600 g / mol

[0349] Synthesis of poly(MMA-stat-2SPV) 91 / 9 mol / mol (M W = 266700 g / mol)

[0350] In a 500 mL autoclave reactor equipped with a water condenser and mechanical stirring, 150 g (299.65 mmol) of methyl methacrylate (MMA) solution (20 wt% in TFE) and 85.87 g (30.23 mmol) of 3-(2-vinylpyridin-1-ium-yl)propane-1-sulfonate (2SPV) solution (8 wt% in TFE) were introduced at room temperature (22 °C). The mixture was degassed by bubbling nitrogen for 60 minutes while raising the temperature of the reaction medium to 60 °C. Further, 4.3 g (0.22 mmol) of AMBN solution (10 wt% in TFE) was introduced under a nitrogen layer. Then, the reaction medium was stirred at 60 °C for 48 hours.

[0351] After polymerization, a sample was taken for 1 1H NMR analysis to determine the conversions of MMA and SPV.

[0352] Results: MMA monomer conversion = 81%, SPE monomer conversion = 86%.

[0353] M W = 266700 g / mol

[0354] Preparation of membranes containing zwitterionic additives

[0355] The membranes were cast from a dope solution containing PVDF 1015 and a blend of the synthesized zwitterionic p(MMA-s-SPE) or (MMA-s-2SPV) copolymer in N-methyl-2-pyrrolidone (NMP) or N,N-dimethylacetamide (DMAc) and immersed in a coagulation bath to induce phase separation (NIPS stands for nonsolvent-induced phase separation).

[0356] General method for preparing the dope solution

[0357] To prepare the stock solution, the zwitterionic additive was dissolved in NMP (or DMAc) at approximately 65 °C and PVDF was added. The resulting mixture was then stirred overnight at 65 °C. Several zwitterionic copolymer:PVDF ratios were fixed at 5 / 95 and 10 / 90 wt. / wt., with a total of 0.5 g of total polymer in 4.5 g of solvent.

[0358] The stock solution was degassed in a vacuum oven set at 40 °C for 24 h. The stock solution was cast onto a glass plate using an adjustable film applicator set to a 200 μm gate size, and the polymer blend was precipitated by immersion in a DI water bath at room temperature for 20 min. After this time period, the resulting film was transferred to a fresh DI water bath and stored at least overnight before use. As a control, a PVDF film without additive was fabricated by dissolving 0.5 g of PVDF in 4.5 g of NMP and following the NIPS procedure explained above.

[0359] Hydrophilicity assessment was performed by contact angle measurement

[0360] Surface hydrophilicity is typically evaluated by the water contact angle (WCA), i.e., by evaluating the contact angle of a water droplet on the sample surface. Due to the absorption phenomenon, this method is not suitable for measuring the contact angle of porous hydrophilic samples, so the contact angle was measured by the Captive Air Bubble (CAB) method. In fact, this method measures the contact angle of a bubble at the surface immersed in a liquid (in this case water), and since the film is already wet, swelling and absorption are suppressed.

[0361] Theoretically, the air contact angle (ACA) and WCA are complementary, meaning that increasing the ACA corresponds to increasing hydrophilicity.

[0362] WCA (°) = 180 - ACA (°).

[0363] Figure 1 Illustrates the principle of the CAB method.

[0364] Air contact angle (ACA) measurements were performed at room temperature using an adapted environmental control chamber filled with deionized water (1) (DI water). Before analysis, the wet sample (2) was wrapped on a 15x15 mm glass substrate and fixed to the sample holder (3) with double-sided tape. The sample was then immersed in DI water, and a 2 μL bubble (4) was dropped onto the sample surface using a J-type syringe (5).

[0365] Contact angle measurements were performed on an optical tensiometer (supplied by BIOLIN) equipped with a high-quality monochromatic cold light LED (6) and a high-resolution (1984x1264) digital camera (7) Performed on Theta Flex). The image acquisition parameters were set to 5 frames per second (FPS) and the minimum acquisition time was 60 s. The instrument was calibrated using a calibration sphere (CA = 143.15°), and the acceptance error was 0.03°.

[0366] The contact angle values obtained were the average of 5 measurements on the same sample. The error bars represent the standard deviation (Std) between the measurements, and the standard deviation was added during the measurement.

[0367] Results

[0368] The results in Table 1 illustrate the appearance differences between the stock solutions, which depend on the molecular weight and composition of the zwitterionic copolymer additive.

[0369] Table 1: Appearance of stock solutions containing PVDF polymer, zwitterionic additive, and NMP.

[0370]

[0371] The results obtained from stock solutions 1 - 3 and 6 - 7 show that for relatively low molecular weight additives, regardless of the composition of the additive, i.e., 95 / 5 or 90 / 10 MMA / SPE (mol / mol), the stock solutions are clear.

[0372] The applicant noticed that for higher molecular weight additives (e.g., Mw > 117000 g / mol), when the composition of the additive is 95 / 5 MMA / SPE (mol / mol), the stock solutions are still clear (see stock solutions 4 and 5, i.e., for Mw of the additive up to at least 173100 g / mol, the stock solutions are clear), but when the composition of the additive is 90 / 10 MMA / SPE (mol / mol), they are unexpectedly turbid (see stock solutions 8 to 14). The same behavior was observed when DMAc was used instead of NMP.

[0373] Turbidity of the stock solutions containing the highest molecular weight additive 90 / 10 MMA / SPE (mol / mol) was observed not only for a PVDF / additive ratio of 90 / 10 (w / w), but also for the prior more favorable PVDF / additive ratio of 95 / 5 (w / w) (see stock solutions 12 - 11 and 14 - 13).

[0374] Not wishing to be bound by any theory, turbidity can be explained by the inhomogeneity of the stock solution caused by the incomplete dissolution of the solid material, which is incompatible with the preparation of membranes by solution casting, either by casting onto a flat support substrate to provide a flat film or by casting to provide a tubular film. In fact, a turbid stock solution may impair the final properties of the flat membrane, e.g., by introducing some defects and membrane inhomogeneities that result in poor mechanical properties or by inducing some phase separation between PVDF and the additive. Moreover, using a turbid stock solution may damage the equipment used to prepare the membrane, e.g., it may cause blockage / clogging when using a spinneret (“spinning method”) to manufacture a tubular film or when casting a flat membrane through a slot die.

[0375] The ACA values measured for PVDF membranes cast from NMP stock solutions with or without copolymer additives are compiled in Table 2 below. As previously mentioned, an increase in the air contact angle (ACA) corresponds to an increase in the hydrophilicity of a given membrane.

[0376] Table 2: Air contact angle (ACA°) measured for membranes cast from NMP stock solutions with additive MMA / SPE 95 / 5 (mol / mol)

[0377]

[0378]

[0379] As can be seen from Table 2, when comparing the ACA values measured for the membrane without any additive (membrane 0) being lower than those of the membranes with additives (membranes 1 to 4), it clearly shows the effect of the additive on the hydrophilicity of the PVDF membrane.

[0380] Moreover, increasing the additive content enhances the hydrophilicity of the membrane (compare membrane 1 with membrane 2 and membrane 3 with membrane 4).

[0381] Finally, a high level of hydrophilicity was obtained using a high molecular weight additive (see membrane 4).

[0382] Based on the above results, the applicant discloses in the present invention a composition comprising a polymer containing VDF and an additive which may be of high molecular weight and contains a certain amount of zwitterionic moieties. The composition is suitable for obtaining a clear dope solution in solvents such as NMP and DMAc and is thus suitable for manufacturing hydrophilic membranes by solution casting. The composition is advantageous: (i) because NMP and DMAc are particularly good solvents for polymers containing VDF (such as PVDF) and are thus very suitable for preparing dope solutions, and in addition they can be recycled; (ii) because the high molecular weight additive contained in the composition is not leached out during the use of the manufactured membrane (such as during aqueous phase filtration) as is the case with lower molecular weight additives; (iii) because the high molecular weight additive contained in the composition does not cause a reduction in the mechanical properties of the manufactured membrane, such as by plasticization, as is the case with lower molecular weight additives.

Claims

1. A composition [Composition (C)], comprising: - at least one vinylidene fluoride (VDF) polymer [Polymer (VDF)], and - at least one copolymer [Copolymer (N-ZW)], comprising (a) Repeating unit [unit (R ZW )] derived from at least one zwitterionic monomer [monomer (A)], wherein, Unit (R ZW ) is derived from at least one monomer (A) selected from the list consisting of: a) an alkyl or hydroxyalkyl sulfonate or phosphonate of a dialkylammonium alkyl acrylate or methacrylate, acrylamide or methacrylamide; b) a heterocyclic betaine monomer; c) an alkyl or hydroxyalkyl sulfonate or phosphonate of a dialkylammonium alkyl allyl; d) an alkyl or hydroxyalkyl sulfonate or phosphonate of a dialkylammonium alkyl styrene; e) a betaine produced from an ethylenically unsaturated acid anhydride and a diene; f) a phosphobetaine having the following formula and g) a betaine produced from a cyclic acetal, and (b) repeating units [unit (R N ))] derived from at least one additional monomer [monomer (B)] different from monomer (A), wherein the unit (R N )) is derived from at least one monomer (B) selected from the group consisting of methyl methacrylate, ethyl methacrylate, butyl methacrylate, methyl acrylate, ethyl acrylate, or butyl methacrylate, wherein, based on the molar composition of the copolymer (N-ZW), the unit (R ZW ) accounts for 0.1 to 5 mol%, and wherein the molecular weight of the copolymer (N-ZW) measured by gel permeation chromatography ranges from 25,000 g / mol to 350,000 g / mol, and wherein the weight ratio of Copolymer (N-ZW) / Polymer (VDF) is at least 3 / 97 and less than 25 / 75.

2. The composition (C) according to claim 1, wherein Polymer (VDF) is selected from addition polymers comprising units derived from VDF and optionally units derived from at least one ethylenically unsaturated monomer different from VDF and containing one or more fluorine atoms, said monomer being selected from the group consisting of: (a) C2-C8 perfluoroolefins; (b) hydrogen-containing C2-C8 fluoroolefins different from VDF; (c) C2-C8 fluoroolefins containing chlorine and / or bromine; (d) having the formula CF2=CFOR f1 a perfluoroalkyl vinyl ether (PAVE), where R f1 is a C1-C6 perfluoroalkyl; (e) A perfluorooxyalkyl vinyl ether having the formula CF2═CFOX0, where X0 is a C1-C 12 perfluorooxyalkyl; and (f) (per)fluorometa-dioxolene having the following formula wherein R f3 , R f4 , R f5 and R f6 each of which is the same as or different from one another and independently is a fluorine atom, a C1-C6 perfluoro(oxy)alkyl group optionally containing one or more oxygen atoms.

3. The composition (C) according to claim 2, wherein, (a) C2-C8 perfluoroolefins are selected from tetrafluoroethylene (TFE), hexafluoropropylene (HFP), perfluoroisobutene.

4. The composition (C) according to claim 2, wherein, (b) The hydrogen-containing C2-C8 fluoroolefins different from VDF are selected from vinyl fluoride (VF), trifluoroethylene (TrFE), hexafluoroisobutene (HFIB), and perfluoroalkyl vinylenes having the formula CH2=CH-R f1 wherein R f1 is a C1-C6 perfluoroalkyl group.

5. The composition (C) according to claim 2, wherein, (c) C2-C8 fluoroolefins containing chlorine and / or bromine are selected from chlorotrifluoroethylene (CTFE).

6. The composition (C) according to claim 2, wherein, (d) having the formula CF2=CFOR f1 The perfluoroalkyl vinyl ether (PAVE) is selected from CF3(PMVE), C2F5 or C3F7.

7. The composition (C) according to claim 2, wherein (e) The perfluorooxyalkyl vinyl ether having the formula CF2═CFOX0 includes the perfluoromethoxyalkyl vinyl ether having the formula CF2═CFOCF2OR f2 , where R f2 is a C1-C3 perfluoro(oxy)alkyl group.

8. The composition (C) according to claim 7, wherein, having the formula CF2=CFOCF2OR f2 The perfluoromethoxyalkyl vinyl ether is selected from -CF2CF3, -CF2CF2-O-CF3 and -CF3.

9. The composition (C) according to claim 2, wherein, In (f), R f3 , R f4 , R f5 and R f6 each of which is the same as or different from one another and independently is -CF3, -C2F5, -C3F7, -OCF3 or -OCF2CF2OCF3.

10. The composition (C) according to claim 2, wherein Polymer (VDF) is a polymer comprising: (a’) at least 60 mol% of units derived from vinylidene fluoride (VDF); (b’) optionally from 0.1 mol% to 30 mol% of units derived from fluorinated monomers different from VDF; and (c’) optionally from 0.1 mol% to 10 mol% of units derived from one or more hydrogenated monomers, all of the above mol% refers to the total number of moles of the units of Polymer (VDF).

11. The composition (C) according to claim 10, wherein Component (a’) is at least 75 mol% of units derived from vinylidene fluoride (VDF).

12. The composition (C) according to claim 10, wherein Component (a’) is 85 mol% of units derived from vinylidene fluoride (VDF).

13. The composition (C) according to claim 10, wherein, Component (b’) is from 0.1 mol% to 20 mol% of units derived from fluorinated monomers different from VDF.

14. The composition (C) according to claim 10, wherein Component (b’) is from 0.1 mol% to 15 mol% of units derived from fluorinated monomers different from VDF.

15. The composition (C) according to claim 10, wherein Component (c’) is from 0.1 mol% to 5 mol% of units derived from one or more hydrogenated monomers.

16. The composition (C) according to claim 10, wherein, Component (c’) is from 0.1 mol% to 1 mol% of units derived from one or more hydrogenated monomers.

17. The composition (C) according to claim 1, wherein, The a) alkyl or hydroxyalkyl sulfonates of dialkylammonium alkyl acrylates or methacrylates, acrylamides or methacrylamides are selected from: - ethyl 3-(dimethylammonio)propyl methacrylate sulfonate, - ethyl 2-(dimethylammonio)ethyl methacrylate sulfonate, - ethyl 4-(dimethylammonio)butyl methacrylate sulfonate, - 2 - (methacryloyloxy)ethyl dimethyl-(3 - sulfopropyl) ammonium hydroxide, - 3 - (acrylamido)propyl dimethyl-(3 - sulfopropyl) ammonium hydroxide, - 3 - (methacrylamido)propyl dimethyl-(3 - sulfopropyl) ammonium hydroxide, - 3 - (acrylamido or methacrylamido)propyl dimethyl-(3 - sulfopropyl) ammonium hydroxide, - 2 - (diethylamino)ethyl 2 - (methacryloyloxy)ethyl sulfopropyl phosphate.

18. The composition (C) according to claim 1, wherein, Said b) heterocyclic betaine monomer is selected from: - sulfobetaines derived from piperazine, - sulfobetaines derived from 2 - vinylpyridine and 4 - vinylpyridine, - 1 - vinyl - 3 - (3 - sulfopropyl) imidazolium betaine.

19. The composition (C) according to claim 18, wherein said b) heterocyclic betaine monomer is selected from 2 - vinyl - 1 - (3 - sulfopropyl) pyridinium betaine or 4 - vinyl - 1 - (3 - sulfopropyl) pyridinium betaine.

20. The composition (C) according to claim 1, wherein, Said c) dialkylammonium alkyl allyl alkyl or hydroxyalkyl sulfonate or phosphonate is selected from sulfopropyl methyldiallyl ammonium betaine.

21. The composition (C) according to claim 1, wherein, Said g) betaine produced from cyclic acetal is selected from ((dicyanoethanolate) ethoxy) dimethylammonium propyl methacrylamide.

22. The composition (C) according to claim 1, wherein, The polymer (N-ZW) contains units (R N ) in an amount of 80 mol% or more, based on the total number of moles of the repeating units of the polymer (N-ZW).

23. The composition (C) according to claim 22, wherein, The polymer (N-ZW) contains units (R N ) that are 90% or more by mole based on the total mole number of the repeating units of the polymer (N-ZW).

24. The composition (C) according to any one of claims 1-16, wherein, Polymer (N - ZW) is a statistical copolymer.

25. Composition (C) according to any one of claims 1-16, said composition (C) being a composition (C L ) which further comprises at least one liquid medium [medium (L)], said at least one liquid medium comprising at least one organic solvent.

26. The composition (C) according to claim 25, wherein the composition (C L ) comprises a total amount of polymer (N-ZW) and polymer (VDF) of at least 1 wt.% based on the total weight of the medium (L), polymer (N-ZW) and polymer (VDF), and / or the composition (C L ) comprises a total amount of polymer (N-ZW) and polymer (VDF) of at most 60 wt.% based on the total weight of the medium (L), polymer (N-ZW) and polymer (VDF).

27. The composition (C) according to claim 26, wherein the composition (C L ) comprises a total amount of polymer (N-ZW) and polymer (VDF) of at least 3 wt.% based on the total weight of the medium (L), polymer (N-ZW) and polymer (VDF).

28. The composition (C) according to claim 26, said composition (C L ) comprising the total amount of polymer (N-ZW) and polymer (VDF) of at least 5 wt.% based on the total weight of the medium (L), polymer (N-ZW) and polymer (VDF).

29. The composition (C) according to claim 26, the composition (C L ) comprises, based on the total weight of the medium (L), the polymer (N-ZW) and the polymer (VDF), at most 50 wt.% of the total amount of the polymer (N-ZW) and the polymer (VDF).

30. The composition (C) according to claim 26, said composition (C L ) comprising, based on the total weight of the medium (L), the polymer (N-ZW) and the polymer (VDF), at most 30 wt.% of the total amount of the polymer (N-ZW) and the polymer (VDF).

31. A method for manufacturing a porous membrane, said method comprising: Step (i): Prepare the composition (C) according to any one of claims 25-30 L ); Step (ii): processing the composition provided in step (i) to provide a thin film; and, Step (iii): processing the thin film provided in step (ii), including contacting the thin film with a non - solvent medium [medium (NS)] to provide a porous membrane.

32. A porous membrane, comprising: - at least one poly(vinylidene fluoride) polymer [polymer (VDF)], and - at least one copolymer [copolymer (N - ZW)], (a) comprising repeating units [unit (R ZW )] derived from at least one zwitterionic monomer [monomer (A)], wherein, Unit (R ZW ) is derived from at least one monomer (A) selected from the list consisting of: a) dialkylammonium alkyl acrylate or methacrylate, acrylamide or methacrylamide alkyl or hydroxyalkyl sulfonate or phosphonate; b) heterocyclic betaine monomer; c) dialkylammonium alkyl allyl alkyl or hydroxyalkyl sulfonate or phosphonate; d) dialkylammonium alkyl styrene alkyl or hydroxyalkyl sulfonate or phosphonate; e) betaine produced from ethylenically unsaturated anhydride and diene; f) phosphate betaine having the following formula and g) betaine produced from cyclic acetal, (b) comprising repeating units [unit (R N )] derived from at least one additional monomer [monomer (B)] different from monomer (A), wherein said unit (R N ) is derived from at least one monomer (B) selected from: methyl methacrylate, ethyl methacrylate, butyl methacrylate, methyl acrylate, ethyl acrylate or butyl methacrylate, wherein, based on the molar composition of the copolymer (N-ZW), the unit (R ZW ) accounts for 0.1 to 5 mol%, and wherein the molecular weight of the copolymer (N-ZW) measured by gel permeation chromatography ranges from 25,000 g / mol to 350,000 g / mol, and wherein the weight ratio of polymer (N - ZW) / polymer (VDF) is at least 3 / 97 and less than 25 / 75.

33. A method for separating an aqueous medium, said method comprising contacting the aqueous medium with the porous membrane according to claim 32.

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